The prior art discloses numerous devices that dissipate mechanical energy in various applications. Examples include protective packaging used in shipping containers, crash helmets, bumpers and vehicular interiors.
Ideally, the most efficient energy absorber exerts a constant resistive force to decelerate an impacting object over a distance that the impacting object deflects the absorber. The most efficient curve would have a constant slope of zero. Elastomeric solids many times act as springs where the force-deflection curve is essentially a straight line of a given slope. Many foam materials display a similar force-deflection curve, although the curves are usually of not of constant slope.
Commonly owned U.S. Pat. No. 5,700,545, entitled Energy Absorbing Structure, discloses an energy absorbing device that offers a nearly constant resistance force over a deflection distance, which if exactly constant, would be theoretically most efficient in absorbing energy. The disclosure of this patent is incorporated herein by reference. Energy is absorbed by a lattice of interconnected strands of material with apertures between the strands, such that upon deformation the strands coalesce and the apertures close.
Commonly owned U.S. Ser. No. 09/018,666 discloses stranded structures that are oriented such that nearly all the metal structure is substantially in the crush plane. The strips of stranded metal are connected by the incident member. This reduces cost and weight of the assembly.
Commonly owned U.S. Ser. No. 09/328,196 describes a structure wherein the stranded metals are assembled into channels in a base and/or a structure of recesses formed in the base. Either or both structures may provide impact protection.
These and other energy absorbing members, in the automobile environment, are used to protect vehicle occupants and must meet the standard for automotive interiors (Federal Motor Vehicles Safety Standard 201) which is incorporated herein by reference. The standard requires that interior components must be tested using a 10 Lbm headform impacting the surface at 15 MPH. A measurement of HIC(d) (head injury criteria) dummy)) is assessed according to a formula set forth in FMVSS 201.
The value of HIC(d) should not exceed 1000 when calculated in accordance with the formula provided by FMVSS201.
The prior art leaves unsolved production problems that stem from relatively expensive and in some cases, less effectual approaches. Injection molding, reaction molding, extruding, blow molding, honeycomb formation, and stranded metal manufacture can be relatively costly. Additionally, it can be difficult to mold very thin wall thickness with some molding technologies.